Xerographic applications

A highly sensitive CdS pigment was also developed for a conventional xerographic application. Optimum xerographic properties were obtained using copper doping at Cu concentrations of 200—300 ppm (26). 

Law (1993) has reviewed the widespread polymorphism in phthalocyanines and its relationship to their photoconductivity and use in xerographic applications. These are best demonstrated by the prototypical copper phthalocyanine CuPc (6-XIX, M = Cu), whose structural chemistry is discussed in detail in Section 8.3.3.1. The polarized absorption spectra of five forms are given in Fig. 6.9. One outstanding feature of these spectra is the rather intense red shifted band at 770 nm in the 5 and modifications compared to the solution absorption at 678nm (Law 1993). This... 

Miscellaneous Forces. Force measurements on polymer surfaces or between chemically modified SFM tips and polymer surfaces yielded important insight into fundamental force vs separation distance relationships for, eg, polymer colloidal particles (207), mechanochemical behavior of individual macromolecules (see section Entropic and Enthalpic Elasticity) (87-96,99), but also adhesion information directly relevant for practical applications, such as electrochemically controlled adhesion (208) or toner particle-rubber interactions relevant for xerographic applications (209,210). 

On the other hand, even in weak CTCs, the completely charge-separated state can be formed at the excited state. Accordingly, photoconductivity could be a first candidate among physical properties influenced strongly by the CT character in wholly aromatic Pis. Photoconductivity of polymers has been widely reported, in particular, with great interest on low molecular weight electron acceptors-loaded poly (vinyl carbazole) for xerographic applications [117,118]. 

For a much more detailed review of the organic photoconductivity, the interested reader is referred to the excellent books by Kao and Hwang [106] and (particularly for xerographic applications) Borsenberger and Weiss [5] and references therein. 

In xerographic applications, the major technology shortfalls for symmetrical squaraines have been the low synthetic yield, high dark-decay and poor spectral response in the visible region, e.g., < 600 nm. Law and Bailey reported efforts to address these issues via unsymmetrical squaraines, such as USq-5 to -15 in Table 10.5 [178]. The precursors for the synthesis, III-V (structures in Scheme 10.3), were synthesized by a [2 + 2] cycloaddition reaction between p-methoxy-phenylketene, or 3,4-dimethoxyphenylketene or 3,4,5-trimethoxyphenylketene with tetraethoxyethylene, followed by a hydrolysis reaction. Unsymmetrical squaraines can then be prepared by condensing III or IV or V with an aniline derivative. The synthetic and absorption spectral data for the synthesized unsymmetrical squaraines are tabulated in Table 10.5. Studies of... 

As with the triarylamines, the triphenylmethanes were first developed for xerographic and photoconductor applications [103], The prototypical example of a material of this type is MPMP (58) shown in Scheme 3.22. 

Mobility measurements by the TOP methods considered in Chapters 3 and 4 are particularly important, but they cannot give information about the whole spectrum of states in the mobility gap of amorphous chalcogenides. Therefore, in addition to TOP, XTOP, IPTOP, TSC, and TSDC, other complimentary techniques that probe the gap states are needed. Xerographic techniques that were initially developed to characterize properties of electrophotographic (xerographic) receptors [1] seemed to be informative, suitable, and widely applicable for the study of amorphous thin films and photoconductive insulator thin films [2],... 

A transfer material has been developed for transferring monochrome and full-color images produced by a xerographic process or a dry toner printing onto a substrate. The process requires the use of a film from TPX as the transfer material. This material is used to transfer the xerographic or dry toner image onto the substrate with the application of heat and pressure (27). 

The first major commercial application of amorphous semiconductors was as the photoreceptor in xerographic copiers and subsequently in laser printers. The early photoreceptors were selenium films, but several other materials were subsequently developed, including ASgSCg and various organic films. Amorphous silicon is a good material for a xerographic photoreceptor (e.g. Shimizu (1985), Pai (1988)) and is used in some commercial copying machines. 

LeComber (1975) showed that by suitable doping, a-Si could be made n- or p-type. These properties, in conjunction with the fact that plasma-deposition processes are generally amendable to large areas, were such that much of the early interest in a-Si was directed to photovoltaic applications (Carlson and Wronski, 1976 Kuwano. 1986). It was quickly recognized, however, that the requirements for photovoltaic applications were, in many respects, similar to those for xerographic photoreceptors. 

From their discovery in 1927 to the present day, the phthalocyanines have been a significant commercial product. These materials have superior colorant characteristics, as well as exceptional stability to heat and light. Today, applications extend from the traditional inks and paints (McKay, 1989) to xerographic photoreceptors (Gregory, 1988, 1991). Because of their importance as colorants, synthetic methods have been developed for their preparation on a large scale (Moser and Thomas, 1963, 1983 Thomas, 1990). Metal-free... 

MAJOR PRODUCT APPLICATIONS plastic magnets, xerographic materials, filters, fibers, energy attenuating powders, microwave absorbing materials... 

Amines are useful building blocks for biological or chemical applications, but were also a core element of polymers and materials for the electronics and xerographic industries. Watanabe et al. synthesized novel bis-(diarylamino)thiophene oligomers (92) and these amines showed intrinsic electronic properties [154]. The employment of the bulky and electron-rich ligand, P( -Bu)3, aided the Pd-catalyzed amination of 2,5-dibromothiophene to bisdiarylaminothiophene (92). 

The absorption, emission, and redox properties of squaraines make them highly suited for applications as photosensitizers. In view of this, the early studies on squaraines were focused on thin photovoltaic and semiconductor photosensitization properties [1,4,5,91-97], Champ and Shattuck [98] first demonstrated that squaraines could photogenerate electron-hole (e-h) pairs in bilayer xerographic devices. Subsequently, extensive work has been carried out on the xerographic properties of squaraines [2,24,34,47,48,99,100], and these properties have been reviewed recently [11]. In an extensive smdy on the correlation s between cell performance and molecular structure in organic photovoltaic cells, squaraines were found to have much better solar energy conversion efficiencies than a variety of other merocyanine dyes [4,5]. 

In many cases it is possible to coat a metal object with a layer of PTFE to meet the particular requirement. Nonstick home cookware is perhaps the best-known example. PTFE is used for lining chutes and coating other metal objects where low coefficients of friction, chemical inertness, nonadhesive characteristics are required. The same properties make PTFE useful for coverings on rollers in food processing equipment, xerographic copiers and saw blades, coatings on snow shovels, and many other similar applications. The Alaskan oil pipeline, for example, rests on PTFE-coated steel plates. Most new bridges and tunnels use similar supports. 

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